The polyolefin industry in the world has greatly developed since the successful development of highly efficient catalysts for polyolefin production in the 1970s. Over the past 20 years, a considerable progress has been made in the catalysts industry which is comparable with the development of the olefin polymerization process. The highly efficient catalysts by virtue of good polymerization performances and mature application technologies still play an important role in the olefin polymerization field. After many exploratory researches over the years, the preparation method of highly efficient Mg—Ti catalysts has been developed from the co-milling method, the suspension impregnation method to the chemical reaction method. Said chemical reaction method has been adopted by various patents relating the use of chemical raw materials such as organo-magnesium compounds, chlorating agents and the transition metal Titanium compounds in preparing various types of catalysts as disclosed in CN1158136, CN1299375, CN1795213, U.S. Pat. No. 3,787,384, U.S. Pat. No. 4,148,754, U.S. Pat. No. 4,173,547, U.S. Pat. No. 4,301,029, U.S. Pat. No. 4,508,843, U.S. Pat. No. 4,921,920 and U.S. Pat. No. 5,124,296. One fatal defect in preparing the Mg—Ti catalysts in such a way is that the forming steps, and thus the shape of the prepared catalyst granules are difficult to be controlled.
In recent development, some materials like emulsifiers are added to the dispersed system of the catalyst precursor comprising Mg/Ti compounds to form an emulsion, and after reaction, the catalyst particles are precipitated out, such that the shape of the obtained catalyst granules can be improved. For example, perfluoropolyether is used in EP0258089A, and perfluorooctane is used in CN 1537118A. The above methods are still of complex forming steps and difficult controlling. The shape of the obtained catalyst granules is also difficult to be controlled, and the used materials are of high cost and difficult to be obtained.
Besides, recent researches show that adding electron donors in preparing a catalyst component can adjust the polymerization activity and the hydrogen response of the catalyst, reduce the oligomers content in the polymerization products, and so on. In CN1129709A, electron donor compounds are used in the preparation of the catalyst to improve the activity and hydrogen response of a catalyst and the block density of polymerization products. The electron donor compounds used in said patent comprises organic compounds with a pair or many pairs of free electrons, mainly organic acid esters.
In conclusion, although various researches have been made in the Zinger-Natta catalyst field, a catalyst of a simple preparation method, an excellent granule shape, a high catalytic activity and a good hydrogen response is still needed in the field.